Category 5 (CAT5) is an Ethernet cable standard defined by the Electronic Industries Association and Telecommunications Industry Association (EIA/TIA). CAT5 cable, which includes four unshielded twisted-pairs of wire, was originally intended to support Fast (100 Mbps) Ethernet and comparable alternatives such as ATM. As with all other types of twisted pair EIA/TIA cabling, CAT5 cable runs are intended to be limited to a maximum recommended run rate of 100 m (328 feet).
The ubiquity and cost-effectiveness of CAT5 cabling make it an attractive choice for video distribution. Hotels and office buildings are perfect environments for video distribution, and are often already wired with CAT5 unshielded twisted-pair (UTP) cable. CAT5 is also cheaper and easier to install than coaxial cable. However, CAT5 cable was originally not intended for high bandwidth video signal applications, since it has substantial attenuation as frequencies increase. In video applications, high frequencies are used to represent both sharp image details and color information. Thus, this attenuation can seriously impact picture quality. Accordingly, there is a need to overcome the high frequency attenuation that occurs when using CAT5 cable, or similar cable, for video signal transmission.
Since unshielded twisted-pair (UTP) cables are now being used for video transmission, companies have begun to design receivers and equalizers that specifically compensate for the high frequency attenuation caused by such cables. One example of this is the EL9110 Differential Receiver/Equalizer available from Intersil Corporation, of Milpitas, Calif. This device accepts a control voltage signal that can be used to set the compensation levels required for different lengths of cable. Thus, if a specific receiver/equalizer is always receiving a video transmission over the same cable of unchanging length, the compensation level at the receiver/equalizer can be manually set once, and video signals should be correctly compensated thereafter. However, a challenge exists where a receiver/equalizer can receive video transmission from various different transmitters, over cables of various different lengths, such as may occur in a building that is wired for video conferencing. In such a case, each time a receiver receives a video transmission over a cable of a different length, the compensation level needs to be adjusted. It would be beneficial if such adjustment could be automatic.